Direct-driven extruder and process for operating the same

Abstract

Depicted is an extruder (1), which converts preferably granular plastic material into the melted state and which comprises at least one

Description

[0001] The invention relates to an extruder, according to the preamble of claim 1, and a process for operating the same.

[0002] Plastic film extruders of the above-described type are used usually to convert plastic raw material into a melted state, which is suitable for further processing. These extruders are used predominantly in extrusion lines, as also presented in the DE 199 31 147.

[0003] The extruder screws are driven with drive units, which are connected either rigidly to the extruder screws via drive unit mechanisms, or impart with the extruder screws the necessary torque via a chain or belt connection.

[0004] The drives used in both cases are expensive and have a large space requirement.

[0005] Therefore, the object of the present invention is to propose a device and a process that render these drives superfluous.

[0006] The problem is solved by means of the characterizing part of claim 1.

[0007] Due to the usually large torque requirement of the extruder screw it is advantageous to provide a drive unit comprising several motors, which can be economical standard drive components. In the interim it is customary in the construction of electric motors to generate high moments and here primarily high starting torques by means of highly polar synchronous or asynchronous motors.

[0008] However, in general the use of direct current drives is also possible.

[0009] Even such motors could be coupled together in order to provide adequate torque. In coupling these modularly built drive units, quick disconnect connecting means can be used in order to react, for example, quickly to changes in the requirements imposed on the torque to be made available, but also to save assembly time. Such connections can also include belts or chains. In arrangements using belts or chains to transfer the torque, the axes of rotation of the rotors and of the extruder screw are not usually in alignment.

[0010] Some examples of connecting means, which facilitate the alignment of the axes of rotation of different rotatable components that are to be connected (rotors and extruder screw), are functional pairs of hollow shafts and pins. However, the irreversible connection of rotatable components or the use of rotors and screws made from one piece is also regarded as relating to the invention.

[0011] When using electric motors, it is adequate to couple the different motors—preferably in parallel—to a common power supply, which can comprise a frequency converter.

[0012] However, it is also possible to use different frequency converters. In this respect the speed of the motor can be controlled; and in the control hierarchy of the different motors, said motor can act as the master. As the control variable for the speed, the melt pressure in the extruder cylinder can be used, for example.

[0013] In such a case the current and/or the torque of the other motors can be controlled or regulated; and the other motors can act as slaves.

[0014] Other advantageous embodiments and applications of the invention follow from the other claims, the description of the subject matter and the drawings. The individual figures depict the following.

[0015] FIG. 1 is a side view of an extruder with a drive unit that comprises one motor.

[0016] FIG. 2 is a side view of an extruder with a drive unit that comprises three motors.

[0017] FIG. 1 depicts an embodiment of an inventive extruder 1, which exhibits a cylinder 6, in which an extruder screw 2 rotates. The extruder screw 2 is held by the bearing 4. The extruder screw 2 is connected rigidly to the rotor 8 of the drive unit 3, which in this embodiment consists of a motor 9. The connecting means of the rotor 8 and the screw 2, which consist here of a pin and a hollow shaft, are not illustrated here. In operation granular plastic material of the extruder is fed via a hopper (not shown here) into the hopper member 5. The plastic melt is extruded via the short extrusion connecting piece 7 and fed usually via suitable feed lines to a plastic film blow head. The latter two components of a blown film extrusion line are not depicted here.

[0018] FIG. 2 shows an equivalently constructed extruder 1, whereby the drive unit 3 comprises here three disk-shaped motors 9, which are arranged in a row and which provide jointly the torque necessary for the rotary motion of the extruder screw. For the purpose of this application a rotor (8) of a motor (9) is considered as the disk armature, when the ratio between the length and the diameter is at least 1:1. The use of such disk armatures is advantageous to generate a high torque for a limited overall length of the drive unit (3).

[0019] In both embodiments electric motors are used as the motors (9). A presentation of the electric feed lines and other power supply devices, such as the frequency converters, was also waived. 1 List of Reference Numerals 1 extruder 2 extruder screw 3 drive unit 4 bearing 5 hopper member 6 cylinder 7 short extruder connecting piece 8 rotor 9 motor 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Claims

1. extruder (1), which converts preferably granular plastic material into the melted state and which comprises at least one

a) cylinder (6), in which an

b) extruder screw (2) rotates, which is connected with a

c) drive unit (3) to at least one motor (9) so that the drive unit (3) provides the torque for the rotary motion of the extruder screw (2),

d) wherein the at least one motor (9) is allocated one or more rotor(s) (8), characterized in that

the extruder screw (2) and the at least one rotor (8) exhibit the same speed in operation:

2. Extruder (1), as claimed in claim 1, characterized in that

the drive unit (3) comprises several motors (9).

3. Extruder (1), as claimed in claim 2, characterized in that

the axes of rotation of the rotors (8) of at least two motors (9) are in alignment.

4. Extruder (1), as claimed in claim 3, characterized in that

the axes of rotation of the rotors (8) of at least two motors (9) and the axis of rotation of the extruder screw (2) are in alignment.

5. Extruder (1), as claimed in any one of the preceding claims, characterized in that

at least one part of the rotating parts (rotors (8) and the extruder screw (2)) are connected together with quick disconnect connecting means.

6. Extruder (1), as claimed in any one of the preceding claims, characterized in that

at least one part of the motors (9) exhibits disk-shaped rotors (8), socalled disk armatures.

7. Extruder (1), as claimed in any one of the preceding claims, characterized in that

the motors (9) are electric motors.

8. Extruder (1), as claimed in any one of the preceding claims, characterized in that

the motors (9) are asynchronous electric motors.

9. Extruder (1), as claimed in any one of the preceding claims, characterized in that

at least one part of the motors (9) of the drive unit (3) is attached to a common frequency converter.

10. Extruder (1), as claimed in any one of the preceding claims, characterized in that

the motors (9) are controlled, whereby the control of the output or input variables of the motors (9) is based on at least one of the following state variables of the extruder (1):

melt throughput of the extruder (1)

melt pressure in the cylinder (6) of the extruder (1).

11. Extruder (1), as claimed in claim 10, characterized in that

the speed of one of the motors (9) is controlled, and that in the control hierarchy of the motors (9), the former is the master; and that the other motors (9) (slaves) are controlled or regulated according to the torque or current.

12. Extruder, as claimed in any one of the preceding claims, characterized in that

the extruder is a part of the extrusion line, such as a blown film extrusion line or a cast film extrusion line.

13. Process for operating an extruder (1), wherein preferably granular plastic material is converted into the melted state and wherein the extruder (1) comprises at least one

a) cylinder (6), in which an

b) extruder screw (2) rotates, which is connected with a

c) drive unit (3) to at least one motor (9) so that the drive unit (3) provides the torque for the rotary motion of the extruder screw (2),

d) wherein at least one motor (9) is allocated one or more rotor(s) (8), characterized in that

the extruder screw (2) and the at least one rotor (8) are driven with the same speed in operation.